Method for enameling tanks



Feb. 9, 1937. w. G. MARTINl 21,070,368

METHOD FOR ENAMELING TANKS Filed June 8,' 19:55 2 sheets-sheet 1 l i :ifJ: ...l

ATTORNEY.

1NVENT0R.

A v Weslgy G Martz'n I BY fw Feb- 9,' 1937- w. G. MARTIN METHOD FORENAMELINQ'TANKS Filed June a, 1935 2 sheets-sheet 2 I FIG. 2.

INVENTOR. Wesley @Martin KfW ATTORNEY.

Patented Feb. 9, 1937 PATENTI oFFlcE MEfrnon Fon ENAMELING TANKS WesleyG. Martin, Milwaukee, Wis., assignor to A. 0. Smith Corporation,Milwaukee, Wis., a corporation of New York Application June 8, 19.35,Serial No. 25,694

' s claims. (ci. sii- 73) This invention relates to the application ofvitreous enamel linings Ito the interiorsof tanks such as are used forthe storage of beer, or milk, or other liquids which would becontaminated by Contact with metal.

An object of the invention is to provide an improved method for theapplication of vitreous enamel coatings to the-interiors of tanks.

A further object of the invention is to provide suitable apparatus foruse in connection with the method.

Other objects of the invention will be clear from the following detaileddescription and the accompanying drawings, in which:

Figure 1 is a side elevation of a tank within a furnace'during thefusing of the enamel;

Fig. 2 is a side elevation, partly in section, of the apparatus used incarrying out the method of this invention, and constitutes an enlargedview of the left hand portion of Figure 1;

Fig. 3 is a top plan view of the apparatus;

Fig. 4 is an enlarged sectional view taken on line tof Fig. 3,; and

Fig. 5 is a sectional view taken on line 5--5 of 25 Fig. 4.

The application of a vitreous enamel lining to the interior of a tankpresents a number of serious diiiiculties. A tank some eleven feet indiameter and thirty feet long has an internal sur- 3 face in excess ofone thousand square feet, and

this surface Y.should `be completely covered with y surface of the tank,and another ring'in order to produce a tank which will be satisfactoryfor the purpose for which it is desired.' 'Due to the large size of thetanks which may be involved, a

40 large expense is involved in an additional firing to cure any defectswhich may exist in apreviously applied coat of enamel. For this reasonit is desirable to have methods available which l will reduce to aminimum the possibility of de- 45 i'ects in an enamel lining of a tank.

One of the objects of my invention is to provide a'method for Aenamelingtanks which will enable a satisfactory lining of enamel to be applied ina single coat. `A single coat lining is .3o preferable to a multiplecoat lining on the ground of greater cheapness, and for someapplications has other points of superiority as well, such as4 lesserthickness and greater resistance to injury by mechanical shock. In somecases a multiple coat lining may be preferred for particular reasons.'I'he methods of this invention are of no less value for the productionoi such multiple coat linings, for it is axiomatic in the enamelingindustry that the ground coat should be as faultless as it can be made.While blisters and cop- 5 perheads or other defects in the ground coatmay sometimes be covered up by the subsequently applied coats of enamel,this by no means invariably occurs. Furthermore, a defective ground coatmay reboll when the other coats are applied 10 and in this way give riseto serious diiliculty in the production of a satisfactory enamel lining.

In my co-pending application for patent, Se rial No. 730,063, iiled June11, 1934, and since issued as U. S. Letters Patent No. 2,004,632, I havel5 disclosed that dimculties which are frequently encountered when anenamel is burned in air may be avoided if the enamel is fused to itsmetal base in an atmosphere substantially devoid of free oxygen; Steelswhich give rise to such vdefects as copperheads or blisters, or whichcause reboiling when the enamel is fused in air, can be satisfactorilyenameled if the enamel is burned in a suitable atmosphere substantiallydevoid of free oxygen as disclosed in my co-pending application. Carbondioxide is an example .of a suitable atmosphere which is disclosed inthat application. l

The present invention is concerned specically with methods and apparatusfor the convenient and rapid expulsion of free oxygen from within thetank which is being fired. In carrying out the method of this invention,it is preferred to first heat'the tank while it is filled with air inorder to produce a lm of oxide on the inner sur- A face of the metaltank, and to then replace the air by a different gas before thetemperature has risen suiciently to fuse the enamel.

According to this invention the air initially within the tank is drivenout and replaced by 40 anotherY .gas by introducing this gas into theheated tank in solid form. This method of `filling the tank with gaspossesses a number of important advantages. The solidied gas is itselfof small volume but expands enormously when it is vaporized in the tank.'Many of the tanks which are enameled on the inside are of veryconsiderable dimensions and have a volume of several thousand cubicfeet. It is desired to drive out the airl and If gas were pumped intothe tank` to drive out the air it would be necessary to either supply alarge pipeleading from the tank to the outside of the furnace in whichit is heated,

. 0r, in case a small pipe is used, to employe. very 55 high gasvelocity.' Neither of these expedients is desirable; By using gas in thesolid form these difficulties .are avoided. The atmosphere desired inthe tank is introduced in condensed form and expands in volume after itis within the tank.

Carbon ,dioxide is an example of a gaseous at- I mosphere which issuitable for the burning of carbon'dioxide blown into the tank tend tosettle to the bottom because of their Weight. Since the tank is hot whenthe solid carbon dioxide is introduced, it is rapidly converted intogas. This will occur at or near the bottom of the tank. Since carbondioxide is a much heavier gas than air it will lie beneath the airinitially within the tank and' rise beneath it. ItV is, of course, notto be expected that there will be no mixing of carbon dioxide gas'withair but it will be readily appreciated that there will be much lessadmixture and much more effective utilizationpf the carbon dioxide if itis introduced at the Abottom of the tank. The openings provided for theexit of air should be located at the top of the tank.

In enameling a tank according to-my improved method, the tank is firstmade and prepared for enameling. In case the tank is fabricated fromsheet steel by electric arc welding with certain kinds of electrodes, itis desirable that the welded tank be treated according tothe methodsdisclosed in my co-pending application, Serial No. 25,695, filed on evendate herewith, in order that no. difficulty may be experienced ingetting the ^enamel to adhere to the electric'arc welds. 'After the'tankhas been' thus treated, the inside is sandblasted, imperfectionsuncoveredin the steel plates are ground out, and the ground patches arepreferably sandblasted again. The sand is cleaned from the tank and acoat of enameling material is applied to its inner surface by anysuitable method, as by spraying. Any suitable enameling material can beused. The coating of enaineling material is then dried. This may beconveniently done by passing a current of filtered air through the tankand heating the outside with alarge gas ame.

Suitable covers are provided for the openings in the tank. These shoulddesirably be made as `tight as possible. One of the openings is providedwith aninlet pipe of sufficient length to reach well beyond the furnacewhen the tank is placed within the furnace for firing. vThe opening towhich the inlet pipe is connected should preferably be near the bottomof the tank. One of the openings at the top of the .tank is providedwith a valve which is originally open to permit the escape y of air butwhich can be closed by a wire leading outside the furnace.

- Thus equipped, the tank is placed on a car and introduced into afurnaoe'for fusing the enamel.`

'I'he inlet pipe extends beyond thev furnace and is connected tosuitable apparatus for introducing solid carbon dioxide chips into the,tank.

Referring to Fig. 1, the `tank I is shown supported on car 2 within thefurnace 3 in which the enamel is fused. 1 'I'he furnace may be heated byany suitable means as by electricity or the combustion of'fuels. Anopening 4 near the bottom of the tank is covered by a manhole cover towhich the inlet pipe 6 is fastened. Another opening I near the top ofthe tank is provided with a valve .8 which can be closed by wire 9. A

smell tube II! is connected to the inlet pipe I5 near the tank. At itsouter end the pipe is .connected to a water manometer I I for measuringthe pressure differential between the gas within the tank and theoutside atmosphere.

The outer end of the inlet pipe t is secured to a connector l2 which'hasa branch inlet I3. The

branch inlet I3 is secured to a hose It for supplying air or other gasunder pressure', and the conlto be shut oi from both.

The apparatus I6 for converting blocks of solid carbon dioxide intochips or shavings and injecting them into the tank comprises a4rectangular box I9 supported on a suitable framework 28. A ilangedopening 2l is provided at the top of the box topermit the introductionof blocks of solid carbon dioxide. into the machine. A cover 22 isprovided to close the box after it is :dlled with carbon dioxide blocks.The cover bears on gasket 23 and is held in place by clamps 24, thusassuring a tight joint.

A plunger 25'tting within the box I9 is carried on a piston rod 25. Apiston 2l secured to the piston rod 26 travels in the air cylinder 28.By means of the valve 29 and ports 30 and 3l, air from a compressed airline 32 can be admitted to either end of the air cylinder 28. The pistoncasing 35. A toothed cylinder :3e is supported within this casing byshaft 3l running in bearings 38. The toothed cylinder is driven in thedirection indicated in Flgs. 2 and 4 by an electric motor 39 supportedon brackets 40. l

The lower side of the cylindrical casing 35 is connected to thefan-shaped outlet il which in turn connects with the tube I5. At theWide end of the outlet 4I is placed a block 42 extending the full widthof the outlet. This block has a longitudinal chamber 43 with whichforwardly directed openings i4 communicate. The rotating cylinder 36 hasteeth provided on its outer surface for shaving chips of carbon dioxidefrom carbon dioxide blocks d5 placed in any suitable way as by a smallgas producer operated under pressure to produce an atmosphere composedessentially of carbon dioxide and nitrogen, or by a compressor forcingue gas into the block 42; or, as indicated in the drawings,

by' a battery of liquid carbon dioxide cylinders 46. These cylinders areconnected through Avalves 41 Aand pipes 48 to a header 49 whichcommunicates with the chamber 43. An orifice or Venturi meter- (notshown in the drawings) may desirably lbe inserted in the line leadingfrom the header 49- to the chamber 43 to indicate the rate at whichcarbon dioxide is being drawn from the cylinders. When carbon dioxide beconnected together so that they can be used in turn.` An excessive drainfrom any one cylinder resultsin a lowering of its temperature and maycause its contents to freeze.

A gas burner 50 supplied with gas by tube 5| may desirably be placedbelow .the box I9 to keep the carbon dioxide blocks 45 from freezing tothe bottom of the box.

Tie rods 52 connected to the framework of the 4 apparatus lead to an eye53 by means of which the whole equipment may be readily lifted with acrane and placed in any desired position.

In using the method and apparatus of this invention, the tank to belined with enameling material is provided with coverings for theopenings and with an inlet pipe 6 as previously described, and is placedupon the car 2. The car is then run in to the heated furnace 3 and thetank begins to heat up. The apparatus for injecting solid carbon.dioxide into the tank is connected to the pipe 6.' As the tank heats upthe air which it initially contained expandsand escapes through theopening 'I and valve 8.

' After the tank has been sufficiently heated to cause the formation ofa thinfllm of oxide on the inner wall of the tank, ythe motor 39 isstarted and air pressure is admitted to the left hand end of the aircylinder 28 toforce blocks of carbon dioxide previouslypplaeed in thebox I9 against the rotating toothed wheel 36. One or more of the valves41 is opened to provide a current of gas from carbon dioxide cylinders46 to blow the chips shaved from the carbon dioxide blocks by therotating cylinder into the tank. The carbon dioxide chips are' vaporizedby the heat of the tank, and the gas which is 'formed forces the air outthrough the valve 8. The

rate of admission of carbon dioxide to the tank is controlled by .themanipulation of valve 29 allowing air to enter the air cylinder 28 andis so regulated that the gas pressure within the the valve 8 is closedby pulling on the wire 9.

'Ihe closure of the valve will greatly diminish the rate at which gascan escape from the tank but there will ordinarily be sufficient leakageto require the continued gradual admission ofcarbon dioxide in order tomaintain the pressure within the tank somewhat above the atmosphericpressure. The gradual admission of carbon dioxide rnay be effected byreducing the rate at which solid carbon dioxide chips are blown into thetank, or the valve I8 may be closed and clean flue gas under pressureadmitted through the valve I1 which is so regulated as to maintain asuitable lpressure within the tank. Flue gas consists predominantly ofcarbon dioxide and nitrogen and when cleaned of solid particles whichmight deposit upon and injure the enamel, is a suitable atmosphere forthe burning of enamelsi but it will not, of course, as rapidly replacethe air Vwithin the tank Aas will carbonl when this stage has beenreached air can be admitted through the valve Il' to maintain a n thetank while it is in a heated condition because this helps to maintainits shape.y

With the particular furnace which has been 5 used, some forty toforty-five minutes was taken for firing a tank about eleven feet indiameter and thirty feet long with walls 1,41 in thickness. About veminutes after the tank was run into the furnace the admission of carbondioxide was l0 begun and was continued at a sufficient rate to maintaina few inches of water pressure within the tank. The valve 8 was closedabout twenty minutes after the tank entered the furnace. This reducedthe rate of escape of gas from the l5 tank. Carbon dioxide was admittedslowly to make good the loss of gas by leakage and to maintain Iwithinthe tank about the same pressure as before. About twenty-*five minutesafter the tank entered the furnace it had reached a 20 temperature ofsome 1500 ,to 1600 F. The valve I1 was closed and a pressure of severalinches of water was afterwards maintained by the-admission of air'. Thefiring was completed in about three quarters of an hour and the tank was25 removed from the furnace to cool. Very satisfactory results havebeen-obtained by the use of this method of firing. Defects whichfrequently occur when air is the atmosphere Within the vtank aresubstantially eliminated. e30

' risen sumciently high to fuse the enamel and thereafter admitting airto the tank to maintain within it a pressure in excess of theatmospheric pressure. y 2. The method of fusing a vitreous enamel 5lining to the interior 'of a tank which comprises heating the tank in afurnace with air in the tank in order to form a layer of oxide on thelnterior of the tank below the coating of enameling material introducingsolid carbon dioxide within 50 the tank to force out the air which itoriginally contained and maintaining a carbon dioxide atmosphere withinthe tank until its temperature has risen suiliciently high to fuse theenamel.

3. The method of fusing a vitreous enamel 55 -lining to a tank whichcomprises heating the 'admitting air to the tank to maintain within it apressure in excess of the atmospheric pressure.

4. In the fusing of a vitreous enamel lining to 55 the interior of atank, the step which comprises replacing air within the tank withanother atmosphere by introducing solid particles of the otheratmosphere into the tank-and thereafter V vaporizing them'to forma gas.70

5. In the fusing of a vitreous enamel lining to the interior of acontainer, the step which comprises replacing air within the containerwith another atmosphere while the container is being heated and beforeit has reached the fusing temperature of the enamel, by introducingsolid. par ticles of the other atmosphere into the container andthereafter vaporizing them to form a gas.

6. In thefusing of a. vitreous enamel lining to the interior of acontainer, the step which. comprises replacing air within the containerwith carbon dioxide gas by introducing solid carbon dioxide into thecontainer and thereafter vaporizing it to form carbon dioxide gas.

7. In the fusing of aL vitreous enamellining to the interior of acontainer, the steps which comprise heating the container with anomdizlng atmosphere therein to form an oxide lm on the inner'surface ofthe container, and thereafter replacing the atmosphere `present in thecontain? er with a diierent atmosphere by introducing solid particles ofsaid diierent atmospherein'to the container and vaporlzing them to formgas'.

8, In the fusing of a vitreous enamel lining to the interior of acontainer, th steps which comprise heating the container with airtherein to form an oxide film on the inner surface of the containerrlandthereafter replacing the air within the container with carbon dioxidegas by introducingesolid particles of carbon dioxide into thecontainierl and vaporizing them to form carbon dioxide" gas.

1 WESLEY G. MARTIN.

